Speed reducer with friction wheel for machines rotating at a high rate of rotation, of the epicycloidal double-train type

ABSTRACT

A friction-wheel speed reducer for machines rotating at high speed of rotation of the epicycloidal double train type employing between a drive rotor (2) and the output shaft (3) of a driven rotor the mechanical drive effects by rotary friction which are obtained by the rolling of friction wheels which are strongly applied against each other. The forces of application are generated by the centrifugal force resulting from the orbital rotation of mass planetaries (5) of mass (M) and propagated from wheel to wheel up to the drive rotor (2) via outer planetaries (6) provided with wheels (62) on the rim of which they rest, the said outer planetaries (6) being disposed to roll while resting on circular tracks (10) via their bearer hubs (61), the movement of rotation being captured by the side cheeks (31) of a planetary-holder cage (30) and transmitted to the output shaft (3) with which it is integral.

The object of the present invention is a speed reducer with frictionwheels in which the force of application necessary for said wheels isproduced by its own operation.

The technical field of the invention is that of devices suitable forcapturing the rotary mechanical energy produced by any driving machine,but more particularly when the speed of rotation of said machine is veryfast, as is true of steam and gas turbines. In fact, for theseturbo-motors, compactness and lightness have as their counterpart veryhigh speeds of rotation exceeding the limit of use of the existingcoupling and reduction means, particularly those with gears.

One device intended for this type of application is already know: it isan epicycloidal induction coupler-reducer for machines of very highspeed of rotation, described in European Patent 0 161 194 in which theelectromagnetic induction is primarily used to capture, at the price ofslippage, the mechanical energy of very high speed of rotation in theprimary part. On the secondary one, another electromagnetic actiontransmits the captured torque, but with the assistance of a purelymechanical rolling and rotary friction effect contributed by thecentrifugal force acting on its inductor satellites, which arerelatively heavy.

The present invention is directed at making an improvement in thisprior-art device by a simple design of better efficiency by avoidingelectromagnetism, since the latter involves not only a difficult andexpensive construction but also, in particular, losses of energy whichcan scarcely be reduced, as a result of slippage, Joule effect,hysteresis and Foucault currents and therefore a substantial release ofheat, which makes cooling means necessary.

The reducer device which forms the object of the present inventionemploys primarily friction wheels which are strongly applied againsteach other by radial forces generated upon the placing in rotation ofits mobile unit.

The use of friction wheels in order to capture and transmit a torque isknown, and numerous friction speed-reducing devices are known, inparticular from French Patent 2 205 974 and its Certificate of Addition2 211 088 which concern a friction epicycloidal reducer which also hasplanetaries, but in which the force of application of the frictionwheels results from the clamping of elastic belts and not from forcesrelated to the operation of the machine as a result of its rotation.

An epicycloidal reducer with centrifugal blocking is also known fromFrench Patent 2 566 868, it having weights which generate a centrifugaleffect, but this effect, which is related to rotation, has the purposethere of obtaining a uni-directional drive in case of reversal of thepower entrance between the primary and the secondary, and not ofproducing the forces of application necessary for friction wheels.

As compared with the process employed in the device according toEuropean Patent 0 161 194 using electromagnetic induction, the presentinvention resides essentially in the means of reversing the direction ofthe centrifugal force generated by the orbital rotation of theplanetaries in order that it also acts, but centripetally, on the driveshaft of high velocity which is located in central position and that,finally, all these primary and secondary friction wheels are appliedrather strongly against each other in order to be able to capture andeffectively transmit the drive torque without slippage, at least to acertain extent, determined, among other factors, by the materialsemployed and the dimensioning selected.

As these friction wheels must be perfectly circular, free of roughnessand non-deformable under the application force and the millingcontinuously suffered in rotation, the use of treated and polished hardsteel is, first of all, adopted in the form, for instance, of ringscoming from "NU" industrial bearings with rollers of specialcase-hardened steel which are perfectly smooth. However, a very lowcoefficient of friction results from this so that a very highapplication force is necessary in order to avoid slippage.

Now, this force must remain well below the mechanical resistance tocompression of the steel selected, subject otherwise to rapidalteration, due to the fact that the resting surface between the wheelsis reduced to a line of metal-to-metal contact. Also, in order toincrease the performance and the mechanical life of the device, the useof other materials having a better coefficient of friction is desirablein order to reduce the application force, then permitting less hardnessor even a state of surface more favorable to an increasing of theadherence. This is why the present invention also covers the use of anymetal other than steel and even of homogenous or composite, more or lesshard non-metallic materials such as plastics, ceramics, elastomers withcarbon fibers or others.

Another feature distinguishes the present invention from the onepreviously described, namely the possible use of booster gears. In fact,in the electromagnetic induction system, the capturing of the drivetorque is necessarily asynchronous due to the relative sliding whichthis system requires between driving wheel (armature) and driven wheel(field magnet); therefore, there can be no coexistence with gears whichgive a synchronous transmission. In the present invention, on the otherhand, as long as there is no slippage all the friction wheels canoperate in synchronism with gears, in the manner of a cog railway.

Now, up to the limit of adherence, the teeth of the booster gearsbacking up the friction wheels theoretically do not bear any torque sothat their threshold of failure is brought to higher speeds of rotation,even with precarious lubrication. It follows from this that thearrangement in accordance with the present invention can be mixed, thatis to say, with gears supplementing the friction wheels in order toeliminate any risk of accidental or fortuitous slippage, in particularupon starting at low speed.

Suitable for all types of drive engines whether faster or slower, andsteam or gas turbines in particular, the arrangement in accordance withthe invention can also be used conversely as speed multiplier from anymotor of low speed in order to drive receivers of high speed ofrotation, such as centrifuges, centrifugal compressors, and the like.

The advantages and characteristics of the present invention will becomeclearer from the following description which refers to the accompanyingdrawing in which one non-limitative embodiment is shown.

In the accompanying drawing:

FIG. 1 is a half cross section through the device according to theinvention;

FIG. 2 is a longitudinal section along the two planes defined by theaxes XOX' of FIG. 1;

FIG. 3 is a transverse geometrical half-drawing showing the arrangement,in principle, of the different friction wheels and masses generatingtheir forces of application, with vector representation of the latter;

FIG. 4 is a half cross section through a second embodiment of thearrangement in accordance with the invention.

Referring to FIGS. 1, 2 and 3, it can be seen that the generalarrangement of the reducer in accordance with the invention is that of aconventional epicycloidal reducer with gears having two planetaryorbits, each wheel of which would have its teeth broken off and bereduced to its pitch circumference, also known as frictioncircumference, all being in contact in pairs, strongly applied by theeffect of the means described below.

The active turning part of the reducer of the invention is containedwithin a cylindrical surrounding recess 1 having two circular rollingtracks 10 of large diameter D5, each fastened concentrically in one ofits two side covers 11.

This turning assembly comprises:

a central drive rotor or primary shaft 2 driven at the speed N0 of thedrive machine by the input shaft coming from the outside, imparting toit the drive torque of rapid rotation to be captured and converted. Thiscentral drive rotor 2 is characterized by the pitch diameter D0 of theraceways which its two bearing hubs 20 has;

a concentric assembly, referred to as satellite-holder cage 30, turningon two ball bearings 34 of the surrounding recess 1, rigidly connectedwith the output shaft 3 debouching to the outside, on the side oppositethe preceding input shaft 2 in order to drive the receiving machine atthe reduced output speed N2. This cage 30 is formed of two side cheeks31 which are firmly connected together and spaced apart by braces 32.

The central drive rotor 2 is supported on its two ends, each providedwith a raceway of diameter D0 by three idle rollers 4 of diameter D1which are arranged 120° from each other, turning freely on three shafts40 located in each of the two side cheeks 31. Thus, each end 20 of thecentral drive rotor 2 rests on these idle rollers 4 at three pointsspaced 120° apart which constitute a rolling bearing, without anyharmful passive resistance, due to the fact that in this way allfriction participates actively in the transmission of the movement.

The satellite-holder cage 30 drives, in orbital rotation, two types ofsatellites or planetaries which constitute the basis of the mechanism:

three satellites of mass M called mass planetaries 5 arranged 120° apartand located 60° on each side of the idle rollers 4 and gravitating on anorbit circle 50, the diameter DM or radius RM of which is determined bythe position of three housings 35 provided in each side cheek 31,receiving their stub shafts or hubs 51 of diameter d2.

six peripheral satellites called outer planetaries 6 of smaller mass m,spaced 60° apart and located 30° on each side of the three massplanetaries 5 for which they serve as support, gravitating on a largerorbit circle 60 of diameter Dm or radius Rm determined by the positionof six open housings 33 provided on the periphery of each cheek 31,receiving their stub shaft or hub 61 of diameter d3.

These six outer planetaries 6 comprise, adjacent to each of their hubs61 of diameter d3, a wheel 62 of larger diameter D3. Each pair of twowheels 62 belonging to two adjacent outer planetaries constitutes one ofthe two rotating support bearings of a mass planetary 5 in concordanceon the cheeks 31 with a housing 35 which has only a positioning rolesince the radial play provided for this recess 35 is such that, inoperation, it does not support any force and therefore is not the seatof any passive resistance. On the other hand, the two tangential forcesof rotary friction exerted on the wheels 62 by the hubs 51 of the massplanetaries 5 participate in the synchronization of their rotation andtherefore in the equi-transmission of the torque of the assembly.

These outer planetaries 6 also rest via their two shaft ends or hubs 61engaged in the half bearings which are constituted by the open housings33, in the bore of the two stationary rolling tracks 10 of diameter D5or radius R5 incorporated in the surrounding casing 1. They rolltherein, strongly sustained by the centrifugal force, their spacingbeing maintained by open housings 33 of the cheeks 31. The tangentialthrust coming from this rolling acts on one side of these half bearings,imparting to it the resultant rotary movement, in the direction of saidthrust, as well as to the cage 30 and to the output shaft 3 which isfastened to it.

The wheels 64 of two adjacent outer planetaries 6, which are not incontact with the mass planetary 5 itself, are in contact with anintermediate idle roller 4 which connects it kinematically to thecentral drive rotor 2.

Thus, the central drive rotor 2, by rotary friction, transmits itsmovement to the idle rollers 4 which transmit it to the wheels 64 andtherefore to the hubs 61 of the outer satellites 6 which roll in the twocircular races 10 of the surrounding casing 1, thus driving thesatellite-bearing cage 30.

Driven in orbital rotation at the speed N2, the mass planetaries 5 turnon themselves at the speed of rotation established by the ratio d2/D0,namely N0 if d2=D0. It is the orbital gravitation of these three massesM which generates the centrifugal force used to apply all the frictionwheels of the apparatus against each other.

Also in orbital rotation at the output speed N2, the outer planetaries 6turn on themselves at the speed of rotation N1. Although less heavy thanthe three mass planetaries 5, the centrifugal force resulting from thegravitation of these six masses m also participates in the mechanicaldrive effects by friction rolling.

The stub shafts or hubs of all the planetaries have races similar tothose of diameter D0 provided on the central drive rotor 2, but theirdiameters--d2 for the mass planetary 5 and d3 for the outer planetary6--can be either equal to D0 or different, the diameter d3 participatingin the ratio of the final reduction, but not d2.

In operation, the radial play of the idle rollers 4 on their pins 40 issuch that the latter do not bear any force as long as said idle rollers4 are self-centered by the symmetry of the radial forces which actthere. These pins 40 therefore also have merely a positioning role, sothat the only passive resistances are located at the two ball bearingsconstituting the supporting bearings 34 for the cage 30 and the six openrecesses 33 of each side cheek 31. The idle rollers 4, as well as thelarge wheels 62 of the outer planetaries 6 constitute intermediatewheels between the hubs 20 of the central drive shaft 2 and the hubs 51of the mass planetaries 5, so that if the diameter d2 of the latter isequal to D0, the mass planetaries 5 rotate at the speed N0 of thecentral drive shaft 2, which may be any speed, due to the fact that,aside from their role of synchronizing the wheels 62, they do nottransmit the movement which they receive to any other.

The choice consisting in having the central drive rotor 2 clamped atthree points 120° apart by 2×3 idle rollers 4 implies the use of threemass planetaries 5 and six outer planetaries 6 and, therefore, angulardivisions of 120°, 60° and 30°, as shown in FIG. 3. The diameter D0 ofthe central drive rotor 2 being selected, the value adopted for that D5of the fixed race determines the geometry of the assembly and most ofthe diameters.

In FIG. 3, d2=d3=D0, but these diameters may be different from D0 andalso from each other. For example, d3 is smaller than D0, which implies,in order to retain the same D1, enlarging D3 accordingly, as well as d2if RM is to remain unchanged; for RM is such that the center of the massplanetaries 5 is located, all radial clearances taken up, at the centerof the equilateral triangle formed by the axis of the central driveshaft 2 and those of the two adjacent outer planetaries 6. In this way,the largest possible diameter is obtained for the cylindrical mass Mborne by each mass planetary 5 and on which there depends, with RM, thevalue of the centrifugal force generated. However, this arrangement isnot necessary, and RM can be smaller to the extent that the spaceavailable in length is compatible with the obtaining of the necessarymass M. Also, the length of the apparatus depends on this factor, takinginto account the width to be imparted to the various friction wheels,the simultaneous search for the least possible volume and a highrigidity of the shafts in very rapid rotation, making it necessary thatthey be as short as possible.

The selection of the diameters d2, d3, D3 and the orbital radius RM alsodetermines the diameter D1 of the idle rollers 4. The radial clearancein the recesses 35 of the stub shafts 51 of the mass planetaries 5permits sufficient reduction of RM to permit the putting in place of allthe wheels 62 of the outer planetaries 6. However, in operation theirenergetic resting on the latter results in slight angular displacementsand slightly different eccentricities, shown in dashed line in FIG. 3.

The device in accordance with the invention operates in the followingmanner: The centrifugal force used to apply the assembly of the frictionwheels against each other comes primarily from the driving in orbitalrotation of the three mass planetaries 5, each of these three radialforces breaking down into two equal symmetrical forces, oblique at 60°,all clearances taken up. While participating in preponderant manner inthe application of the hubs 61 of the outer planetaries 6 against theirrace 10, the force resulting from these two oblique forces acts incentripetal direction on the central drive shaft 2.

However, the six outer planetaries 6 which are also driven in orbitalrotation also generate a centrifugal force Fc" which is proportional totheir own weight m and eccentricity Rm but which, being radial, does notcarry back towards the central drive shaft 2. In addition, byconstruction, this weight m is not as great as the weight M of the massplanetaries 5 so that, despite a much larger orbital drive radius, thissecond centrifugal effect is substantially less. Nevertheless, it addson to the force of the application received from the masses M by thehubs 61 rolling in the bore of the two stationary races 10.

Each of the mass planetaries 5 resting against the rolling supportbearing which the large wheels 62 of the two adjacent outer planetaries6 constitute for it, the centrifugal force developed radially breaksdown into two equal oblique symmetrical 60° vectors which tend to movethem apart from each other. It follows that each tends to approach thefollowing outer planetary 6, which also, together with its neighboringone, is subjected to the same spreading effect by the second massplanetary, and so on for the others.

Now, this approaching two by two of the outer planetaries 6 is limitedby the presence, resting against each of the two wheels 62, of theintermediate idle roller 4, which is thus pushed towards the center bythe two equal convergent forces, the result of which is a centripetalradial force. Thus, while participating in preponderant manner inapplication on the races 20 of the hubs 61 bearing the outer planetaries6, the centrifugal force generated by each of the three mass planetaries5 is transmitted in the direction towards the center in three equalvectors 120° apart by the idle rollers 4 resting against the rings 20 ofthe central drive rotor 2. The latter is then clamped as in a three-jawchuck so that, while being supported by the idle rollers 4, as in abearing, it transmits to them its rotation at high speed by the effectof rotary friction.

There is thus constituted an active bearing which dispenses with anyother and which, at the same time, permits the capturing of the drivetorque on said shaft, which means is substituted for the electromagneticinduction effect previously used.

Secondly, the drive by rotary friction is effected by the six outerplanetaries 6 and also differently, due to the fact that the force ofapplication cumulates here two distinct centrifugal effects, namely thatgenerated by the mass planetaries 5 and that inherent in the weight m ofeach outer planetary 8.

The forces at play in the arrangement in accordance with the inventionare as follows: Let the vector Fc be of radial direction, the size ofwhich corresponds to the centrifugal force generated by each massplanetary 5; it breaks down into two equal and symmetrical vectors Fc',each directed towards the center of the outer planetaries 6 located onopposite sides, forming an angle of 60° with the initial vector Fc. Theparallelogram of forces being thus formed of two equilateral triangles,it follows that these two vectors Fc' are equal in size to Fc.

Each of the forces Fc' is transmitted to the outer planetaries 6 byresting against their large wheels 62 and it can therefore be translatedat their center in accordance with the direction defined by the line ofthe centers passing through the point of contact on the large wheel 62of the corresponding hub 51 of the mass planetary 5. The vectors Fc'break down there then into two forces: the one radial force Fa pushesthe hub 61 of this outer planetary 6 against the race 10 and acts on therace 10, thus producing a resting reaction Ra which is equal and ofopposite direction; the other, Rp, exerts a thrust in the direction ofthe adjacent outer planetary 6, perpendicular to the vector Fc'previously translated.

The two forces Ra and Rp which are applied at the center of the outerplanetary 6 in question can be composed in direction of the point ofrolling contact between the large wheel 62 and the idle roller 4,forming a resultant Rf which can be brought back to the center of thelatter, connecting there with another equal force Rf coming from theadjacent outer planetary 6 in accordance with the same scheme. From thecomposition of these two convergent vectors Rf, there finally resultsthe radial force Er acting on the central drive rotor 2. It is easy toverify that this resultant force is twice the initial centrifugal forceFc, namely Er=Fc×2.

In the previous arrangements employing electromagnetism, the inductorsatellites roll directly in the bore of the race, but here, withidentical general dimensioning, the mass planetaries 5 are necessarilyon a circular orbit which is reduced approximately by half, as well astheir own diameter and therefore their weight; the centrifugal force towhich they are subjected is therefore four times less.

Now, in the place of three inductor satellites, we now have six outerplanetaries 6 which roll on the stationary race 10, subjected to thesame orbital drive at the output speed N2 but with a weight m which isless than M: the centrifugal force generated Fc" is therefore alsoreduced, but a certain compensation takes place due to the fact that itacts on twelve rollers instead of six and that the resting force of thebearing rollers 61 of each outer planetary 6 is the sum Q=Fa+Fc".

For these friction wheels, it is absolutely necessary to avoid anyrelative slipping or skidding, subject otherwise to premature andrapidly prohibitive wear. This condition of it not sliding depends onthe coefficient of friction resulting from the nature and condition ofthe surfaces in rolling contact, their lubrication, and the pressureexerted by one on the other. Thus the force of application Er at thelevel of the central drive shaft 2 between its rings 20 clamped betweenthe idle rollers 4 may be very different from that, Q, which applies thehubs 61 of the outer planetaries 6 against the stationary race 10.

The drive torque capture capacity by the primary of the apparatusdepends on the friction conditions of the first, while the transmissioncapacity by its secondary depends on those of the second; now, theforces of application Er and Q result from the size of the weights m andM so that the obtaining of equivalence between the capture capacity andthe transmission capacity leads to optimizing the ratio M/m.

This result can also be obtained by a smaller orbital radius RM, whichleads to increasing D3 and has the result of reducing not only Fc butalso Fc', with a smaller decrease of M; this solution is to be adoptedif it is desired to increase the reduction ratio in which the diameterD3 participates.

If the weight M is to be increased while the preceding dimensioning andthe new choice of RM do not permit greater volume, this planetary can bedesigned with a hollow body weighted with very dense metal, for instancelead.

Booster gears can be adopted for the sole purpose of avoiding theskidding of the hubs 61 of the outer planetaries 6 upon their rolling inthe races 10 by means, on each of them, of a pinion 63 of pitch diameterd3 acting on an inner gear 12 of pitch diameter D5. One can alsocontemplate mechanical connection between the three mass planetaries 5and the six outer planetaries 6 by means of a train of ratio d2/D3 witha low if not zero working rate. Finally, in order to avoid any possibleslippage, in particular in case of sudden variation of the speed, andtaking into account the inertia of the mass planetaries 5, a connectioncan be contemplated by a train of ratio d2/D0 between these last threeand the central drive rotor 2, the rate of work being here also zero incontinuous established speed so that, despite the size of the values ofthe speeds of rotation, these accompanying toothings must hold, evenwith precarious lubrication.

The present invention therefore makes it possible to discharge the gearteeth of a reducer operating at very high speeds of rotation by transferof their work to friction wheels so that they only have to play a roleof synchronization and possible boostering. Furthermore, this systemavoids any construction constraints of fixed bearings. Furthermore,being rolling, they are active here due to the fact that the passiveresistances participate in the transmission of the movement.

It is to be noted also that all of these rotors and planetaries turnwhile resting on each other via friction wheels the diameter of which isprecisely the pitch diameter of their accompanying gears, so that therelative positioning of the latter is always perfect, while, on theother hand, the lubrication play of the conventional bearings has arepercussion on the meshing play, which is affected to a greater orlesser extent thereby.

The reduction ratio is established in the following manner: Thekinematic chain starts from the central drive shaft 2, turning at thehigh speed N0, and leads, via the cage 30, to the output shaft 3 whichrotates at the reduced speed N2. It passes successively over thefriction wheels characterized by their diameter from D0 to D1, from D1to D3 which is fastened to d3, from d3 to the cage 30 by the tangentialthrust resulting from the rolling of d3 on D5; therefore, only thediameters D0, D3, d3 and D5, and not d2 or D1, participate in theexpression of the reduction ratio.

The first speed reduction takes place between the rings 20 of thecentral drive shaft 2 rotating at N0 and the large wheels 62 of theouter planetaries 6 via idle rollers which are of a diameter D1=D0, thediameters D0 and D3 intervening so that the speed of rotation of thelatter and their attached hubs 61 is N1=N0×D0/D3 or N0=N1×D3/D0.

The second reduction of speed takes place between the previous hubs 61of diameter d3 rotating at the speed N1 and the race 10 on which theyroll, driving the cage 30 along in this movement at the speed N2. For anordinary reducer, one would have an output speed N2=N1×(d3/D5) so thatN0/N2=(D3/D0)/(d3/D5), namely N1=N0×(D0/D3) or N0=N1×(D3/D0) andN2=N1×(d3/D5).

But as a planetary system is concerned, this ratio is to be increased ordecreased by 1 depending on whether the direction of rotation of thedriving shaft 2 and of the output shaft 3 are the same or opposite, sothat finally, N0/N2=(D3×D5)/(D0×d3)±1.

If one now refers to FIG. 4, one can note in said figure anotherembodiment of the reducer in accordance with the invention. In the firstembodiment, in fact, although connected to the drive rotor by a gearingtorque, the mass planetaries do not play any role in the reduction ofspeed. They are only subjected to turning on themselves in synchronismwith the wheels on which they rest. However, it is due to them and thetwo series of three idle rollers that the directions of rotation of theprimary and secondary are finally reversed and, therefore, the reductionratio decreased by 1.

In the second embodiment, in order to find concordant directions ofrotation and benefit from the better reduction ratio, the mounting ismodified as follows.

The two series of three idle rollers 4 serving as bearing for the driverotor are replaced by two series of three other rollers 4' of muchsmaller diameter, that of the hubs of the mass planetaries. Theserollers are still in rolling contact with the large wheels 62 of theouter planetaries 62 and, as previously, constitute their limitingspacing stop. However, due to their reduced diameter and the moreeccentric position of their bearing shaft, they are no longer in rollingcontact with the hubs 20 of the central drive rotor 2, thus losing theirformer role of carrying bearing, which has devolved upon two series ofsix additional rollers 7.

These additional rollers 7 are intermediate wheels inserted in theannular space left around the central drive rotor 2, which are carriedwith play by shafts implanted in each side cheek 31 of the cage 30. Itfollows that the number of bearing rollers of the central drive rollerpasses from two series of three at 120° to two series of six at 60°,namely six rolling points supported instead of three, as previously.

The rolling contacts between these two series of six rollers 7 and thetwo series of three rollers 4' which are more eccentric are located oneach side; in the case of a first group of three at 120°, between thehubs 20 of the drive rotor 2 and the series of three idle rollers 4'pushed centripetally each by a pair of large wheels 62 of two outerplanetaries 6 which rest there; in the case of the second group of threeothers, also at 120° but alternating with the previous ones, between thehubs 20 of the central drive rotor 2 and the hubs 51 of the massplanetaries 5, the assembly of these rollers 7 also resting on the twoseries of rollers 4' each pushed centripetally by a pair of large wheels62 of two consecutive outer planetaries 6.

This mutual resting is permitted by the direction of the synchronousrotations thus obtained.

The resultant centripetal force received from a pair of large wheels 62by the roller 4' on which they rest therefore is no longer directlyapplied on the corresponding hub 20 of the central drive rotor 2. Itacts along two oblique and symmetrical directions on two intermediaterollers 7 which are 60° apart.

Now, each of these two rollers 7 constitutes a double support under theeffect of these thrusts, on the one hand on a hub 20 of the drive rotor2 and on the other hand on a hub 51 of a mass planetary 5, so that thesetwo hubs oppose their being further apart from each other.

The assembly being thus statically balanced, it results therefrom thatthe same thrust, supported by each of these rollers, is pushed backradially on each hub of the drive rotor in centripetal direction.

Finally, each hub of the drive rotor is thus clamped in six points at60° by the same centripetal force coming from the centrifugal forcegenerated by the three mass planetaries. The result is the same as inthe first embodiment, but as the direction of rotation of the drivenshaft becomes that of the driving shaft, the reduction ratio is greater,being increased by 2 for equal wheel diameters.

Furthermore, the doubling of the number of points of rolling contact onthe drive rotor is beneficial, dividing by 2 the unit resting pressure,so that these mass planetaries can be made heavier in order to increasethe capture- transmission capacity of the driving shaft.

Furthermore, due to the presence of an intermediate friction wheelbetween the hub of the drive rotor and the hub of the mass planetary,which is maintained strongly applied in the force system thus organized,the benefit of the rigorous maintaining of the gearing clearances byconstant application between wheels having the pitch diameter of thepinions extends to the now triple train of the accompanying gearsconnecting these rotors.

In the first embodiment, the case of the double train between driverotor and each mass planetary is all the more critical since it turnsvery rapidly and the driven pinion necessarily moves away from thedriver located at the center as a result of the taking up of all themounting plays between wheels; hence, an eccentricity which inevitablyincreases the gear play.

Finally, the gearings may be all combined on the same side; theorganization of their lubrication is easier and the lengthwise spacetaken up is substantially reduced.

The complication introduced being more apparent than real, this secondembodiment may be preferred for these advantages, particularly if ahigher reduction ratio is necessary.

I claim:
 1. A planetary friction speed reducer comprising:an input driverotor, an output shaft, a plurality of idle rollers, a plurality of massplanetaries orbiting the input drive rotor, a further plurality of outerplanetaries engaging the mass planetaries and an outer stationary race,each of the outer planetaries having a large diameter wheel portion anda small diameter hub portion, each of the wheel portions engaging one ofthe mass planetaries and one of the idle rollers, each of the hubportions engaging the outer stationary race, a planetary cage retainingthe outer planetaries in an axial and a radial direction andtransmitting rotational movement to the output shaft, the massplanetaries having a small freedom of movement in the radial directionand possessing a predetermined mass which is larger than the mass of theouter planetaries such that rotational movement imparted to the inputdrive rotor causes the mass planetaries to move radially outward therebyincreasing the normal force of all engaging surfaces within the speedreducer.
 2. A speed reducer according to claim 1, wherein the massplanetaries are formed as metal, hollow bodies, the hollow bodies beingfilled with a metal or higher density than the metal of the hollowbodies.
 3. A speed reducer according to claim 1, including a boostergearing means for providing an additional drive path.
 4. A speed reduceraccording to claim 3, wherein the booster gearing means is providedbetween the hub of the outer planetaries and the outer stationary ring.